Previous studies show that the administration of procaine to bipolar and borderline patients gives rise to a diversity of behavioral responses ranging from euphoria to dysphoria. Since procaine is believed to selectively stimulate the limbic structures of the brain, it is reasoned that these behavioral differences might result from neuroclinical differences in these regions of the brain. To test the hypothesis that alcohol might alter limbic function we administered procaine to alcoholics, patients with panic disorder, panic patients with alcoholism and controls. Our results show that patients with panic disorder were more likely to experience a panic attack following procaine than were controls. Preliminary analysis of our results suggest that changes in vagal tone do not completely explain the rise in pulse frequency seen during a panic attack.